tf_approx: Inter- and extrapolation functions for 'tfd'-objects
In tf: S3 Classes and Methods for Tidy Functional Data

tf_approx_linear

R Documentation

Inter- and extrapolation functions for `tfd`-objects

Description

These are exported evaluator callbacks for tfd objects. They control how function values are inter-/extrapolated to previously unseen arg values and are used by tf_evaluate().

In typical use, set an evaluator when constructing a tfd (tfd(..., evaluator = tf_approx_linear)) or replace it later via tf_evaluator(x) <- tf_approx_none.

These helpers are wrappers around zoo::na.fill(), zoo::na.approx(), etc. and all share the same signature (x, arg, evaluations), so they can also be called directly.

The list:

tf_approx_linear for linear interpolation without extrapolation (i.e., zoo::na.approx() with na.rm = FALSE) – this is the default,
tf_approx_spline for cubic spline interpolation, (i.e., zoo::na.spline() with na.rm = FALSE),
tf_approx_none in order to not inter-/extrapolate ever (i.e., zoo::na.fill() with fill = NA)
tf_approx_fill_extend for linear interpolation and constant extrapolation (i.e., zoo::na.fill() with fill = "extend")
tf_approx_locf for "last observation carried forward" (i.e., zoo::na.locf() with na.rm = FALSE)
tf_approx_nocb for "next observation carried backward" (i.e., zoo::na.locf() with ⁠na.rm = FALSE, fromLast = TRUE⁠).

For implementing your own, see source code of tf:::zoo_wrapper.

Usage

tf_approx_linear(x, arg, evaluations)

tf_approx_spline(x, arg, evaluations)

tf_approx_none(x, arg, evaluations)

tf_approx_fill_extend(x, arg, evaluations)

tf_approx_locf(x, arg, evaluations)

tf_approx_nocb(x, arg, evaluations)

Arguments

`x`	new `arg` values to approximate/interpolate/extrapolate the function for.
`arg`	the `arg` values of the `evaluations`.
`evaluations`	the function values at `arg`.

Value

a vector of values of the function defined by the given (x_i, f(x_i))=⁠(arg, evaluations)⁠-tuples at new argument values x.

Examples

x <- tfd(matrix(c(0, 1), nrow = 1), arg = c(0, 1))
tf_evaluate(x, c(0, 0.5, 1))
tf_evaluator(x) <- tf_approx_none
tf_evaluate(x, c(0, 0.5, 1))

tf_approx_linear(
  x = c(0, 0.5, 1),
  arg = c(0, 1),
  evaluations = c(0, 1)
)

tf documentation built on April 7, 2026, 5:07 p.m.